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In this work, we test the ability of an exact solution, found in the framework of a nonlinear extension of the Israel–Stewart theory, to fit the supernovae Ia, gravitational lensing, and black hole shadow data. This exact solution is a generalization of one previously found for a dissipative unified dark matter model in the context of the near-equilibrium description of dissipative processes, where we do not have the full regime of the nonlinear picture. This generalized solution is restricted to the case where a positive entropy production is guaranteed and is tested under the condition that ensures its causality, local existence, and uniqueness. From the observational constraints, we found that this generalized solution is a good candidate in the description of the observational late-time data used in this work, with best-fit values of H 0 = 73.2 − 0.9 + 0.8 k m / s M p c , q 0 = − 0.41 − 0.03 + 0.03 , ξ ^ 0 = 0.88 − 0.17 + 0.09 , ϵ = 0.34 − 0.04 + 0.03 , and k = 0.27 − 0.20 + 0.37 , at a 1 σ (68.3 %) of confidence level. We show that the nonlinear regime of the Israel–Stewart theory consistently describes the recent accelerated expansion of the universe without the inclusion of some kind of dark energy component and also provides a more realistic description of the fluids that make up the late universe. [ABSTRACT FROM AUTHOR]

In this work, we test the ability of an exact solution, found in the framework of a nonlinear extension of the Israel–Stewart theory, to fit the supernovae Ia, gravitational lensing, and black hole shadow data. This exact solution is a generalization of one previously found for a dissipative unified dark matter model in the context of the near-equilibrium description of dissipative processes, where we do not have the full regime of the nonlinear picture. This generalized solution is restricted to the case where a positive entropy production is guaranteed and is tested under the condition that ensures its causality, local existence, and uniqueness. From the observational constraints, we found that this generalized solution is a good candidate in the description of the observational late-time data used in this work, with best-fit values of H0=73.2−0.9+0.8km/sMpc, q0=−0.41−0.03+0.03, ξ^0=0.88−0.17+0.09, ϵ=0.34−0.04+0.03, and k=0.27−0.20+0.37, at a 1σ(68.3%) of confidence level. We show that the nonlinear regime of the Israel–Stewart theory consistently describes the recent accelerated expansion of the universe without the inclusion of some kind of dark energy component and also provides a more realistic description of the fluids that make up the late universe.

The causal dissipative model is a plausible choice to explain the late accelerated epoch of the universe. At the same time, Λ CDM is considered the standard model to explain the cosmological data corresponding to the late evolution of the universe. We consider a bulk viscous model in which dissipation is driven by the bulk viscosity ζ = α ρ 1 / 2 , described using the full causal Israel-Stewart theory. We computed the model parameters using the latest observational data (Pantheon). We contrasted this model with Λ CDM model for the late accelerated phase using the Bayesian inference method. The Bayes factor was obtained by calculating the likelihood for Pantheon data. Suitable prior values were assumed for model parameters to calculate the likelihood. It shows that the evidence for Λ CDM against this viscous model is very strong according to the Jeffreys scale. [ABSTRACT FROM AUTHOR]

In this paper we find exact analytic cosmological solutions for a relativistic dissipative fluid, in the framework of the causal Israel–Stewart theory. We use a general expression for the relaxation time, which is related with the bulk viscosity coefficient, the energy density and pressure of the fluid, and non-adiabatic contribution to the speed of sound. Through the factorization method we find some new exact parametric solutions for the special case s = 1 / 2 . For each solution the deceleration parameter, the energy density, the dissipative pressure, the entropy, and the ratio between the dissipative pressure and the fluid's pressure are evaluated as a function of the cosmic time. We finally discuss the kinematic behavior of the solutions and their relationship with their thermodynamic behavior. [ABSTRACT FROM AUTHOR]

We show that the recently formulated causal and stable first-order hydrodynamics has the same dynamics as Israel-Stewart theory for boost-invariant, Bjorken expanding systems with an ideal gas equation of state and a regulating sector determined by a constant relaxation time. In this case, the general solution of the new first-order formulation can be determined analytically.

In this work we study wave propagation in dissipative relativistic fluids described by a simplified set of the 2nd order viscous conformal hydrodynamic equations corresponding to Israel–Stewart theory. Small amplitude waves are studied within the linearization approximation while waves with large amplitude are investigated using the reductive perturbation method, which is generalized to the case of 2nd order relativistic hydrodynamics. Our results indicate the presence of a “soliton-like” wave solution in Israel–Stewart hydrodynamics despite the presence of dissipation and relaxation effects. [ABSTRACT FROM AUTHOR]

Abstract: The uniform shear flow (USF) under the thermally relativistic limit is discussed on the basis of Truesdell’s theory of the USF for the nonrelativistic gas, when the Lorentz contraction is negligible. We investigate the solution of the USF under the thermally relativistic limit using the pseudo Maxwellian molecule. Under the thermally relativistic limit, solutions of seven moment equations for the USF, which are obtained from Grad’s 14 moment equations by Israel–Stewart, violate the positivity of the pressure tensor, when the dimensionless truncation number is larger than the threshold value owing to the contribution of the dynamic pressure, whereas solutions of six moment equations for the USF never violate the positivity of the pressure tensor. [Copyright &y& Elsevier]

Abstract: Relativistic thermodynamics is derived from kinetic equilibrium in a general frame. Based on a novel interpretation of Lagrange multipliers in the equilibrium state we obtain a generic stable but first order relativistic dissipative hydrodynamics. Although this was believed to be impossible, we circumvent this difficulty by a specific handling of the heat flow. [Copyright &y& Elsevier]

Abstract: The stability of the ()-dimensional solution of Israel–Stewart theory is investigated. Firstly, the evolution of the temperature and the ratio of the bulk pressure over the equilibrium pressure of the background are explored. Then the stability with linear perturbations is studied by using the Lyapunov direct method. It shows that the shear viscosity may weaken the instability induced by the large peak of bulk viscosity around the phase transition temperature . [ABSTRACT FROM AUTHOR]